Billions of dollars are spent each year to control insects, and additional billions of dollars are lost because of crop damage inflicted by insects. Synthetic organic chemical insecticides have been the primary tools used to control insects, but biological insecticides are playing an important role in some areas. Insect-resistant plants transformed with insecticidal protein genes, such as the insecticidal proteins derived from Bacillus thuringiensis (B.t.), have revolutionized modern agriculture and heightened the importance and value of insecticidal proteins and their genes.
Toxin Complex (TC) proteins and genes, found primarily in bacteria of the genera Photorhabdus and Xenorhabdus (but also in other bacterial genera such as Serratia, Pseudomonas, and Paenibacillus) are an important, relatively new source of insecticidal proteins and genes. There are at least three distinct classes of TC proteins. Native Class A TC proteins are approximately 280 kDa in size and possess insecticidal activity. Class B TC proteins (approximately 170 kDa) and Class C TC proteins (approximately 107 kDa), in combination, enhance the insecticidal potency of Class A TC proteins but possess little to no insecticidal activity in the absence of a Class A TC protein. That is to say, Class B and Class C TC proteins in combination potentiate the insecticidal activity of Class A TC proteins. See e.g. US-2004-0208907 and WO 2004/067727 for a more detailed review of the art. Class A TC proteins possess insecticidal activity, but this activity is relatively low. When a Class A TC protein is combined with a Class B and a Class C TC protein, they form a complex that is much more potent than the Class A TC protein alone.
Unlike Bacillus thuringiensis, Xenorhabdus, and Photorhabdus, which are organisms that are known to be insecticidal and to have insecticidal proteins, organisms such as Fusarium graminaerum (now known as Gibberella zeae) and Methanosarcina were not known to be insecticidal and were not known to produce insecticidally active proteins.